The manufacture of a vehicle tire commonly includes the steps of forming a tire carcass, forming a belt and tread portion of the tire separately of the carcass, and thereafter marrying the belt and tread portion of the tire to the carcass to form a "green" tire. The green tire is thereafter treated to form the tread and various other features of the tire. Other supplementary steps, such as stitching, may be performed during the course of or following one or more of the aforementioned steps.
Formation of the belt and tread portion of the tire is accomplished on a belt and tread drum. Such a drum has an outer cylindrical surface, or circumference, about which one or more layers of tire belt material (comprising, for example, reinforcement cords embedded in a polymeric binder) are laid, and subsequent to the laying down of the tire belt material, the belt material is overlaid with one or more layers of strip tread material to comprise a "package".
The belt and tread drum is rotatably mounted about a central longitudinal axis, and the several layers that make up the belt and tread package are laid onto the drum as it is rotated. The circumference of such a drum is preferably capable of expanding and contracting to, for example, accommodate the removal of a completed package (which is essentially nonexpandable radially) from the drum circumference and to enable a single drum to be used to form belt and tread packages of alternative diameters. The circumference of such a drum can be collectively comprised of a plurality of rigid arcuate segments wherein each segment provides an arc of the cylindrical surface and is mounted for movement toward and away from the longitudinal axis of the drum to accommodate the adjustment in drum circumference. Furthermore, each segment is preferably provided with a plurality of fingers which cooperate, or mate with, the fingers provided in an adjacent segment so that as the circumference of the drum is expanded and contracted, the cooperating fingers render the perimeter of the cylindrical surface usefully continuous.
In the manufacture of a vehicle tire, a carcass is formed on a drum in a manner somewhat similar to the forming of a belt and tread package so that the drum used in forming a tire carcass may employ the concepts of the present invention. Further, after the carcass has been formed, it is transferred to a second stage drum and held thereon while a belt and tread package is transferred from the belt and tread drum onto the outer circumference of the carcass employing a transfer ring. Thereafter the belt and tread package is married to the carcass. The transfer ring commonly employed comprises basically an inverted belt and tread drum. That is, whereas the outer circumference of the belt and tread drum is adjustable to accommodate the formation of the belt and tread package thereon and to permit the removal therefrom of a completed belt and tread package, the inner circumference of the transfer ring is adjustable to permit the ring to encompass the outer circumference of the belt and tread package and contract in diameter to cause the segments of the transfer ring to engage and grasp the belt and tread package for transferring of the package to the carcass of the tire.
It follows, however, that the radius of curvature of the are of the drum's outer cylindrical surface or the transfer ring's inner circumference provided by their respective accurate segments are each fixed by the rigidity of the segments, thus rendering it impossible for the segments to be moved between two radial positions and collectively provide perfectly-formed cylindrical surfaces at each of the two positions. If, for example, the circumference of the drum is adjusted to a size at which the segments are positioned at a distance from the longitudinal axis which exceeds the radius of curvature of each segment arc, there will exist, transitional regions, or "spots", about the drum circumference where the surface is relatively flat, thus rendering the drum out-of-round. If these flat transitional regions are large enough (as is likely in the case when the drum is expanded to accommodate a tire of relatively large diameter), the drum is likely to produce undesirable "flat-spotting" effects on a tire constructed with the drum, wherein these flat spotting effects are a consequence of the severity of radial runout during the construction of a tire component upon the drum. Such flat-spotting effects are undesirable in that they are known to adversely affect tire performance. The size, and thus the effects, of these flat spots can be reduced by increasing the number of segments about the drum circumference to thereby provide a greater number of segments through a given arc of the cylindrical surface. However, the mechanical structure mounted internal of the drum needed to support the segments for movement radially of the drum prevents the increase in the number of segments beyond a practical limit. Flat-spotting is also a problem associated with prior art transfer rings in that the newly-formed belt and tread package is sensitive to deformation by contact with the segments of the transfer ring and the flat spots are "imprinted" into the outer circumference of the belt and tread package. These imprints later show up as irregularities in a finished tire.
It is therefore an object of the present invention to provide a new and improved belt and tread drum of the aforedescribed class wherein flat-spotting effects produced with the drum are substantially reduced.
Another object of the present invention is to provide such a drum wherein the severity of the out-of-round condition of the drum when its circumferential surface is expanded to relatively large diameters is appreciably lessened.
Another object of the present invention is to provide such a belt and tread drum having circumference-providing segments which are uncomplicated in construction and effective in operation.
It is another object of the present invention to provide an improved device for grasping the outer diameter of a tire component or carcass and having reduced flat-spotting tendencies.
It is another object to provide a multi-segmented expandable/collapsible apparatus for grasping the inner diameter or the outer diameter of circular or ring-type objects which are sensitive to alteration of their diameter by reason of flat-spotting of their diameter when grasped.
It is another object of the present invention to provide a multi-segmented transfer ring for use in the manufacture of vehicle tires.